This invention relates to a method of treatment of waste water containing sulfur compounds such as thionic acid ions, particularly to a method of treatment of a blowdown water issued from a wet type desulfurization apparatus for waste flue gas.
Wet type desulfurization apparatus for the waste flue gas which use limestone slurry as an absorbent produce calcium sulfate (CaSO.sub.4) as a by-broduct through a reaction of sulfur dioxides in the waste flue gas with the limestone slurry and an oxidation of its resulting product. The limestone slurry from which the CaSO.sub.4 is separated is cyclicly used as the absorbent so that soluble impurities included in the limestone slurry and the waste flue gas are condensed in slurry during its recirculation. Therefore, it is necessary to blow off a part of the slurry as a blowdown water. In the blowdown water, substances contributing to COD (chemical oxygen demand), such as thionic acid ions are included and the COD is raised through recirculation of the slurry, so that the blowdown water can not be issued out of the wet type desulfurization apparatus without suitable treatment.
It is known that dithionic acid ions are decomposed by heating them in an acid solution. By simple application of the method to the treatment of the blowdown water, however, the substances can not be effectively and economically treated, because the content of the substances varys according to the length of times of the circulation, concentration of the sulfur dioxide and kinds of compositions and quantities of dust included in the waste flue gas, and the COD also varys.
Accordingly it is desirable to provide a method such that the substances contributing to the COD can be effectively and economically decomposed and the blowdown can be issued.